The present invention relates to a mobile radio telephone network system and, in particular, to a location registration system for registering a location of a radio telephone set in the mobile telephone network system.
A mobile telephone network system of the type described generally comprises a telephone line and a plurality of radio telephone sets. The radio telephone sets are movable or travel in an area which is divided into a predetermined number of zones.
A plurality of radio connection devices or radio communication devices are assigned to the respective zones. Now, providing that all radio telephone sets are alive, that is, capable of always carrying out communication, and are moving among the zones, some of the radio telephone sets can use the radio connection device assigned to the zone in which the radio telephone sets in question are present at a time.
Between the telephone line and the radio connection devices, a line connection unit or a line control unit is connected for controlling communication between the telephone line and the radio connection devices. In detail, the line connection unit connects the telephone line with a particular one of the radio connection devices assigned to a particular one of the zones in which a particular one of the radio telephone sets is present at a time, in order to enable the particular radio telephone set to carry out communication with the telephone line through the particular radio connection device and the line connection unit.
In order to enable the line connection unit to select the particular one among the radio connection devices, the line connection unit must hold location information therein which is indicative of a particular zone number of the particular radio connection device in which the particular radio telephone set is present.
To this end, the mobile telephone network system has a location registration system.
In a conventional location registration system, the line connection unit has a subscriber's file for memorizing a list of the telephone numbers or identification (ID) numbers of the radio telephone sets and numbers of zones in which those radio telephone sets are present. Each of the radio telephone sets has a key which is operated by a user of the radio telephone set. When the user operates the key of the particular radio telephone set, the particular radio telephone set transmits a location registration request signal. One or more of the radio connection devices receive the location registration request signal as received request signals, respectively, and detect electric field strength or level of the received request signals. That is, those one or more radio connection devices serves as receiving devices. The receiving devices form modified request signals by adding the electric field strength signal and the zone numbers assinged to those receiving devices to the received request signal, and transmit the modified request signals to the line connection unit. The line connection unit receives those modified request signals and compares the electric field stregths in the modified request signals with one another. Then, the line connection unit decides a particular one of the modified request signals which has the highest one of the electric field strengths and registers the zone number in the particular modified request signal together with the telephone number of the particular radio telephone set into the subscriber's file. Thus, it is possible to renew the location information of the radio telephone sets registered in the subscriber's file in the line connection unit.
However, it is impossible to renew the location information of the radio telephone sets in the subscriber's file, if the user does not operate the key in his radio telephone set when his telephone set travels.